The present invention relates to nut-and-screw mechanical actuators, or jack mechanisms, of the type disclosed in U.S. Pat. No. 3,485,110, issued Dec. 23, 1969, and U.S. Pat. No. 3,178,958, issued Apr. 20, 1965, which includes a housing having a ball nut component rotatably mounted therein and driven by an input worm shaft which extends into the housing and engages a worm gear associated with the ball nut component. The ball nut component is formed with a helical cavity and exteriorly mounted ball return tubes in which a plurality of balls are circulated in a constant driving engagement with the helical grooves of a screw member extending through the ball nut component.
When the actuator is operated at high speeds and under relatively high torque loads, wear becomes a significant problem and there is also a problem of heat generation at the meshing gear drive, which conditions require a substantial amount of lubrication. Moreover, because of practical construction considerations, the ball nut component includes a plurality of individual elements which are assembled as a unitary structure, and this unitary structure includes a number of joints and the like which are not fully sealed, whereby it has heretofore been impractical to expose the exterior surface of the ball nut component, and the aforementioned meshing gear drive therefor, to a lubricating oil because such oil would leak through the ball nut component to the screw member and ultimately be lost.
Accordingly, it is now common practice to substantially fill the housing area surrounding the ball nut component with a heavy grease (e.g. Ep-2 grade grease). This grease acts, of course, as a lubricant between the moving gear drive parts, and, because of its high viscosity, there is no significant leakage of the grease through the ball nut component. However, grease has several disadvantages. First, at very high speeds of the input drive shaft, the heat build up is sufficient to break down the grease whereby wear will occur between the gear drive parts, and, as a result, the mechanical actuator cannot be run at high speeds for any significant period of time. Additionally, the viscosity of the grease reduces substantially the ability of the grease to circulate freely among the moving parts and throughout the housing interior, and, consequently, the lubricating capacity of the grease is impaired and the overall thermal efficiency of the mechanical actuator is reduced by the inability of the grease to transfer heat from the gear drive parts to the housing wall for dissipation.
It has also been heretofore proposed in U.S. Pat. No. 3,858,458, issued Jan. 7, 1975, to form the housing interior of a ball nut-and-screw actuator with an oil compartment provided with a vertically extending dam or barrier and an overflow passageway in such dam, all of which retains the oil at a level in the housing which is isolated, by gravity, from the ball nut and screw arrangement. However, the oil compartment is not sealed, and the actuator must be maintained at a substantially vertical disposition at all times to prevent oil leakage through the ball nut and screw arrangement. Furthermore, the height of the actuator must be extended appreciably and undesirably to accommodate the dam or barrier.
In accordance with the present invention, a mechanical acutator is provided which includes a unique gear-nut assembly and housing arrangement that permits lubricating oil to be used both to lubricate the moving parts of the gear-nut assembly and to dissipate heat from such moving parts, regardless of the particular disposition of the actuator during use.